L6711 datasheet(19/38 Pages) STMICROELECTRONICS

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L6711

Offset automatically given by the DAC selection or by VID5 when VID_SEL=SGND differs from the offset

implemented through the OFFSET pin: the built-in feature is trimmed in production and assures ±0.5%

error (±0.6% for the Hammer DAC) over load and line variations while implementing the same offset

through the OFFSET pin causes additional errors to be considered in the total output voltage precision.

When the Integrated Thermal Sensor is enabled (see Figure 12 and following section), the pin programs,

in the same way as before, a negative offset. This is to compensate the positive native offset introduced

by the ITS. The effect of the programmed offset on the output voltage results (IOFFSET is now added to IFB

and no more subtracted as before):

Offset resistor is designed to compensate the ITS native offset as described in the following section.

The Offset function can be disabled by shorting the pin to SGND.

Figure 12. Voltage Positioning with Integrated Thermal Sensor

8.3

INTEGRATED THERMAL SENSOR

Current sense elements have non-negligible temperature variations: considering either inductor or LS

mosfet sense, the sensing elements modify proportionally to varying temperature. As a consequence, the

sensed current is subjected to a measurement error that causes the regulated voltage to vary accordingly.

To recover from this temperature related error, a temperature compensation circuit is integrated into the

controller: the internal temperature is sensed and the droop current is corrected (according to a scaling

external resistor RTC) in order to keep constant the regulated voltage.

The ITS circuit subtracts from the IFB current a current proportional to the sensed temperature as follow

(see Figure 12, Only the IDROOP and ITC contributes to IFB have been considered):

where

where A and B are positive constants depending on the value of the external resistor RTC (see Figure 13),

TJ is the device junction temperature and TMOS is the mosfet (or the used sensing element) temperature.

The resistor RTC can be designed in order to zero the temperature influence on the output voltage at a

fixed current as follow:

OFFSET

1.240 V

------------------- R

⋅

OUT

VID

FB IOFFSET

⋅

–

VID

1.240

OFFSET

-------------------------

⎝⎠

⎛⎞

⋅

–

VID

–

1.240V

1:1

VTC=A+B·(TJ-25)

RTC

ROFFSET

OFFSET

1:1

IDROOP

VID

COMP

VSEN

64k

FBR

FBG

64k

RFB

To Vcore

(Remote Sense)

IOFFSET

OUT T,IOUT

()

VID

SENSE TMOS

()

------------------------------------------- I

OUT

TC TJ

()

–

⋅

–

TC TJ

()

-----------

–

()

⋅

[]

⋅

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